In general, in a mobile communication system, transmission delays of signals from mobile stations UE at a radio base station eNB differ depending on the difference between the distances to the radio base station eNB from the respective mobile stations UE. For example, a transmission delay of a signal from a mobile station UE located at a cell edge is larger than a transmission delay of a signal from a mobile station UE located near the radio base station eNB.
In a radio access scheme such as “LTE (Long Term Evolution)” which has been promoted by the 3GPP for standardization in recent years, if timing differences of receiving signals (each being an uplink data signal, a control signal or the like) from mobile stations UE at a radio base station eNB are within a certain range (a Cyclic prefix length given to each information symbol in a radio sub-frame), the signals from the respective mobile stations UE are orthogonal to each other. Thus, it is determined that a synchronization state is established in an uplink for each mobile station UE.
Specifically, in the above radio access scheme, if an uplink dedicated resource (for example, a PUCCH: Physical Uplink Control Channel) is set up, the radio base station eNB can measure an offset between reference reception timing, and reception timing of a control signal (for example, a Sounding Reference signal, CQI information, or a Scheduling Request) transmitted from each mobile station UE by use of the uplink dedicated resource, and thus can determine whether or not a synchronization state is established in an uplink for each mobile station UE.    Non-patent Document 1: 3GPP TSG RAN WG1 Meeting #47bis R1-070106 (Jan. 15, 2007)